Advancing optical communications have made optical fiber communications networks have long optical paths and complicated branches. Accordingly, the switching of optical fiber paths (transmission paths) between telecommunications circuits has increased in optical communications apparatuses and light transmission apparatuses, resulting in using many optical switches. The purposes of switching optical paths are not only to switch usual telecommunications circuits, but also to recover from troubles by switching a broken transmission path to another normal path, to conduct the maintenance of the switching of optical telecommunications network lines in buildings and areas, to change optical paths in measuring apparatuses, etc. With respect to the branching number of optical paths, there are a 1×2 optical switch for switching one movable optical fiber to two stationary optical fibers, a 1×m or n×m optical switch in which ends of many optical fibers are abutting, etc.
With respect to the switching systems of optical switches, there are a system of switching light-proceeding directions by electrically or optically changing the refractive index or phase of optical paths, a system of switching light-proceeding directions by mechanically moving optical paths, etc. Among them, mechano-optical switches are advantageous in that they suffer little coupling loss of light and have little dependency on the wavelength of transmitted light. Accordingly, proposals have been made to provide mechano-optical switches having various structures depending on various switching purposes and branching numbers.
For instance, a mechano-optical switch described in U.S. Pat. No. 6,169,826 comprises, as shown in FIG. 11, a movable member 30 made of a soft magnetic ceramic, to which end portions of two movable optical fibers 20a, 20b are fixed, a stationary member 32 fixed at a position opposing the movable member 30, four stationary optical fibers 21a, 21b, 21c, 21d fixed to the stationary member 32, an actuator for moving the movable member 30 relative to the stationary member 32, and a means for positioning the movable optical fibers 20a, 20b relative to the stationary optical fibers 21a, 21b, 21c, 21d, the actuator comprising a permanent magnet 52, first and second yokes 50a, 50b opposing each other such that they sandwich the movable member 30 in its moving direction, and coils 51a, 51b mounted to the first and second yokes 50a, 50b. This small, high-reliability mechano-optical switch is now widely used.
Optical telecommunications networks are classified to telecommunications networks of analog lines (called “telecommunications lines”) including long-distance communications between cities, and closed telecommunications networks in companies, etc. [generally called “local area networks (LAN)”]. Some telecommunications networks of analog lines have optical fibers for redundant circuits to minimize troubles by the disruption of optical fibers, with many optical switches used for switching between these optical fibers for redundant circuits. Optical switches for this purpose have a self-holding mechanism consuming electric power only during switching but needing no electric power when optical fibers are coupled. Described in U.S. Pat. No. 6,169,826 as an optical switch suitable for such applications is a latching optical switch comprising movable optical fibers which are moved by energizing coils and held at that position by a permanent magnet.
The LAN-type optical telecommunications network has a closed light loop as a whole, with optical fibers connected by terminal devices on the loop. Introduced light signals are once converted to electric signals, and electric signals passing through copper lines from the terminal devices are subjected to necessary treatments for transmitting to or receiving from a LAN, converted to light signals and then return to the loop. Though there is no problem in this telecommunications network as long as each terminal works normally, the failure of one terminal stops light signals from being sent, resulting in the breakdown of the entire telecommunications network. To prevent this problem, an optical switch for cutting the failed terminal away from the light loop at the time of abnormality should be provided. In this case, a non-latching optical switch in which movable optical fibers automatically return to a predetermined “home position” when a normal electric signal is stopped is more preferable than the above latching optical switch in which movable optical fibers are kept at a holding position. Though the optical switch described in U.S. Pat. No. 6,169,826 has a small, high-reliability structure using an electromagnetic force for switching operation, it is not a non-latching type. It may be contemplated to use a spring force for returning without electric power, but the structure of the electromagnetically operated optical switch described in U.S. Pat. No. 6,169,826 would become complicated if a spring mechanism is added thereto.